Tesseract is now included better thresholding (binarization) in v5. Users that have
thresholding issues should try that first. If we find further problems
this can be brought back as a plugin.
When compiled without pybind11 2.8.0, pikepdf supplies a shim to implement
pikepdf._ObjectMapping.values() which has subtly different semantics
from a true dict-like objects; in particular it supports
next(objectmap.values())
where a standard dict requires
next(iter(objectmap.values()).
pybind11 2.8.0 now implements .values() properly, meaning some misuses of
protocol in ocrmypdf fail.
If pybind11 < 2.8.0, pikepdf will
continue to offer its shim. If pybind11 >= 2.8.0, pikepdf does not add its shim.
Consequently no changes were needed in pikepdf.
Closes#843
Acrobat insists that PDF/A-1b should not have object streams.
Other programs like veraPDF disagree with this restriction, but
we can accommodate Acrobat so we will.
Also add more tests around this.
Previously if we found vectors of any sort on a page, we would bump
the DPI up to 400. We did nothing
about pages with text. As a result,
pages with a low image resolution
and printable text would have the text downgraded to image
resolution when --force-ocr was used.
We don't try to determine if the text is visible or invisible OCR text, since
that is a slower test. --redo-ocr would improve such cases anyway.
Previously we produced a raster image, then multiplied image width
by DPI to get the page size. However if there is rounding the
page size may not match exactly. In this modified approach we
constrain the page size to match.
Our method of getting data from pdfminer would silently consume a StopIteration
if pdfminer returned no processed pages, leading to odd error message.
We improve an error from pdfminer properly, and returning a more
descriptive error of our own.
It would be possible for ocrmypdf to repair the file before sending it to
pdfminer, but this seems to be rare enough that we won't do that yet.
James R. Barlow
Dima KuznetsovandGitHub